Method to Improve Release Characteristics of Elastic Polyolefin Fibers

ABSTRACT

The present invention relates to a method for reducing the amount of die buildup associated with the production of polyolefin based elastic fiber and for improving the unwind or release characteristics of such fiber. In particular the method involves the use of polydimethylsiloxane (PDMSO) in the polyolefin resin.

The present invention relates to a method for reducing the amount of diebuildup associated with the production of polyolefin based elastic fiberand for improving the unwind or release characteristics of such fiber.In particular the method involves the use of polydimethylsiloxane(PDMSO) in the polyolefin resin.

There has been much recent publicity related to cross-linkedpolyolefin-based elastic fibers, including the news of the Federal TradeCommission establishing a new generic term, “Lastol”, to cover suchfibers. The production and make-up of these fibers are known in the art,for example as described in U.S. Pat. Nos. 6,048,935; 6,140,442;6,194,532; 6,248,851; 6,448,355; 6,436,534; 6,500,540; and 6,559,208,all of which are incorporated by reference in their entirety.

In the production of these fibers, it has been observed that depositsgradually build up on the dies during melt spinning. Periodically, theproduction must be shut down in order to remove these deposits. It istherefore desirable to reduce or eliminate these build-ups.

After the fiber has been formed, the fiber is typically wound on bobbinsor spools for later use. Another problem which has been observed withsome of these packages is that the fiber tends to stick to the packageduring unwinding leading to tangles and breaks. It is a goal of thepresent invention to improve the release or unwind characteristics ofthe fiber from these packages.

It has been discovered that the addition of small amounts ofpolydimethylsiloxane (PDMSO) to the polyolefin fiber prior to fiberformation aids in both of these goals. This result is unexpected assilicones are generally applied to the fiber externally by means of ametering pump or, a kiss roll. Such oils are commonly called spinfinishes.

FIG. 1 is a graph demonstrating the frequency dies needed to be cleanedusing different levels of PDMSO.

FIG. 2 is a graph demonstrating the effect of PDMSO and lubricating oilon the releasability factor.

FIG. 3 demonstrates the load at break and elongation at break of fibersmade in accordance with the present invention.

The present invention is a way of improving the fiber spinning andunwinding properties for any polyolefin-based fiber. The olefin polymerfor use in the present invention can be any olefin based materialcapable of forming a fiber, including ethylene-alpha olefininterpolymers, substantially hydrogenated block polymers, propylenealpha olefin interpolymers (including propylene ethylene copolymers),styrene butadiene styrene block polymers,styrene-ethylene/butene-styrene block polymers, ethylene styreneinterpolymers, polypropylenes, polyamides, polyurethanes andcombinations thereof. The homogeneously branched ethylene polymersdescribed in U.S. Pat. No. 6,437,014 (which is hereby incorporated byreference in its entirety), particularly the substantially linearethylene polymers, are particularly well suited for use in thisinvention.

The present invention is particularly useful for fibers made form linearlow density ethylene alpha-olefin copolymers, most preferably thosehaving a density in the range of 0.80 to 0.89 g/cc (as determined byASTM 1505) and a melt index from 0.5 dg/min to 10 dg/min (as determinedby ASTM D1238). Preferred polyolefin materials are sold under theAFFINITY trade name by The Dow Chemical Company, the EXACT trade namesold by Exxon-Mobil Company, or the TAFMER trade name sold by MitsuiChemical Company. The most preferred polymer is polyethylene with anoctene comonomer content of 5 to 30 percent by weight, having a densityof about 0.875 g/cc and a melt index of about 3 dg/min.

The PDMSO used can be a hydroxyl-terminated, ultra high molecular weightpoly(dimethylsiloxane). The PDMSO preferably has a molecular weight ofapproximately 2 million. The PDMSO is conveniently added to the polymercomposition in the form of a masterbatch, in a polyethylene basedcarrier material, in an amount so that the final composition containsfrom 0.1 percent to 5 percent PDMSO by weight, more preferably from 0.3percent to 2 percent by weight. Most preferably the final compositioncontains should contain no less than 0.5 percent by weight PDMSO.

The PDMSO can be added to the polymer in any way known to the art. ThePDMSO is ideally added prior to extrusion/fiber formation in order toget the benefit of both reduce die build-up and improved unwindingcharacteristics, but may be added after fiber formation, for example ina spin finish, if only improved unwinding performance is desired.Conveniently, the PDMSO may be added to the polyolefin material via amasterbatch with additional polyolefin material as the carrier medium.

The addition of the PDMSO reduces die build-up in the extrusion of thepolymer and also improves the release characteristics of the fiber fromthe packages or spools of the fiber. This latter effect can be furtherimproved with the external application of a spin finish. The spin finishcan be any lubricating oil and is preferably selected from the groupcomprising silicones, mineral oils, ester oils with a viscosity range of1 to 120 cSt, and blends thereof.

The method of the present invention leads to spools or packages havingimproved unwinding or release characteristics. In order to demonstratethis improvement a releasability test was created. For this test, thepackage/spool was placed in contact with a feed or drive roller(friction roller) rotating at a set speed (as provided by spinning thegiven roller at a speed of 30 rpm), and the filament was unwound onto awinding roller initially rotating at a speed set at three times thespeed of the feed roller (that is the draft was 3×). At this speed anddraft, no sticking was observed. The winding roller rotational speed wasthen gradually reduced until the point where the unwinding fiber sticksas indicated by the fiber no longer being removed tangentially from thepackage/spool. A releasability factor (“RF”) was then calculatedaccording to the following formula where “r.s.” means rotational speed:${RF} = \frac{\begin{matrix}{{\left( {{r\quad.\quad s\quad.\quad{of}}\quad{winder}{\quad\quad}{at}{\quad\quad}{point}{\quad\quad}{sticking}\quad{observed}} \right)\quad -}\quad} \\{\left( {{r\quad.\quad s\quad.\quad{of}}{\quad\quad}{feed}{\quad\quad}{roll}} \right) \times 100}\end{matrix}}{\left( {{r.s.\quad{of}}\quad{feed}\quad{roll}} \right)}$

Fibers with the best releasability have very low values on this test(that is they do not stick even at low speeds). It is preferred that themethod of the present invention reduce the release-ability value by atleast twenty percent (for example if the release-ability factor for aparticular fiber was 80 percent without the use of PDMSO, then themethod of the present invention will preferably result in areleasability factor of 66 percent or less).

Another aspect of the present invention is an elastic polyolefin-basedfiber package having a releasability of less than 100 percent, morepreferably less than 50 percent, most preferably less than 30 percentusing the test just described.

EXAMPLES

For these Examples fiber was prepared from a base polymer prepared usingan INSITE Constrained Geometry Metallocene catalyst. The base polymerwas polyethylene with an octene comonomer content of about 35 percent togive a density of 0.875 g/cc with a melt index of 3.0+/−0.20 dg/min asdetermined using ASTM D1238.

A masterbatch of 40 percent by weight PDMSO in an ethylene styreneinterpolymer was prepared. The master batch was then dry blended intothe base polymer to provide the desired level of PDMSO in the fiber. Forthese examples 3 levels of PDMSO were evaluated, 0 percent. 0.5 percentand 1 percent. The polymer was then melt spun into fibers at a melttemperature of 270° C. Each polymer formulation was run for 8 hours andthe number of times the spinnerets (dies) had to be cleaned is reportedin FIG. 1.

As can be seen from FIG. 1, the frequency of cleaning required droppedsignificantly with the presence of PDMSO.

As the fiber was spun, it was wrapped onto packages. In some cases anexternal spin finish of silicone lubricating oil (Takemoto DELION 9535)was applied in an amount of 1.6 percent by weight to the fiber prior towinding onto the package. These packages where then evaluated for theirrelease-ability using the test method described above. An improvement of35-40 percent in the release value was obtained with PDMSO (indicated as“Si” in the figure) alone compared to filament with no lubrication andan improvement of up to 70 percent was observed for PDMSO in combinationwith external spin finish oil. The results of these experiments arereported in FIG. 2.

The load at break (as determined by DIN 53 835 Part 1 and elongation atbreak (as determined by DIN 53 835 Part 1) of these fibers were measuredat 100 mm grip distance at 500 nm/min separation speed. There was nosignificant loss of physical properties when using this internal andexternal lubrication method, as demonstrated in FIG. 3.

1. In a method for the production of elastic polyolefin-based fiberswherein a polyolefin-based material is extruded and melt spun into afiber, the improvement comprising incorporating an amount ofpolydimethylsiloxane (PDMSO) into the polyolefin-based material.
 2. Themethod of claim 1 wherein the polyolefin-based material comprises anethylene alpha-olefin copolymer produced using a Metallocene catalyst.3. The method of claim 2 wherein the alpha olefin is octene.
 4. Themethod of claim 3 wherein the polyolefin-based material has a density inthe range of 0.8 to 0.89 g/cc and a melt index in the range of 0.5 to 10dg/min.
 5. The method of claim 2 wherein the PDMSO has an averagemolecular weight of approximately 2 million.
 6. The method of claim 1wherein the PDMSO is added in an amount such that the PDMSO comprisesfrom 0.1 to 5.0 percent by weight of the fiber.
 7. The method of claim 6wherein the PDMSO is added in an amount such that the PDMSO comprises0.5 to 1 percent by weight of the fiber.
 8. The method of claim 2wherein the PDMSO is added via a masterbatch.
 9. The method of claim 2further comprising an additional step of adding a lubricating oil to theformed fiber via a spin finish.
 10. The method of claim 1 characterizedin that the method results in a releasability factor which is at least20 percent less than a similar fiber without PDMSO.
 11. A fiber packagehaving a releasability factor less than 50 percent.